In the field of fluid machinery applications, there is an increasing demand for improving the robustness and operation of the components making up the fluid machinery system. In the present context, the term “fluid machinery application” refers to any arrangement that can extract energy from a continuously moving stream of fluid (liquid or gas). Since the fluid machinery application transfers the energy from the fluid to a rotor, and typically is provided with a rotating component through which the fluid passes, the fluid machinery application should be capable of supporting a radial force and a considerable large axial force, as seen in the direction of the rotor shaft of the fluid machinery application. The energy from the fluid streams is converted into mechanical energy of a rotating shaft by one or several turbines. In this type of applications, the rotating component typically refers to the rotor, which is provided with a set of vanes or blades.
One example of a fluid machinery application is a wind turbine arrangement. Other examples of fluid machinery applications are water turbine arrangements and propulsion turbine arrangements. Depending upon the purpose of the fluid machinery application, the working fluid may be either liquid or gas.
In order to support the rotational movement of the rotor, this type of arrangements is typically provided with one or several bearings. Due to the large dimensions and weight of wind turbines, the load bearing capabilities and performance of the bearing(s) supporting the rotor shaft and the wind turbine blades is of high importance. As a consequence, the bearing must be aligned and positioned in a correct manner in order to avoid unnecessary wear of the components making up the bearing.
Typically, for a wind turbine of horizontal, or near horizontal, rotor shaft type, the bearing arrangement must support both axial and radial loads, wherein the axial loads refers to axial loads transferred from the turbine blades during operation as well as axial loads arising from the weight of the rotor shaft and turbine blade arrangement, which is often mounted with a tilted angle in relation to the horizontal plane in order to reduce the risk of collision between the turbine blades and the wind turbine tower.
Moreover, the weight and size of the components as well as the location of the rotor arrangement in tower-like structures increase the cost for manufacturing, mounting, and servicing of the wind turbines. In particular, the attachment of load bearing rolling bearings to the rotor shaft and to support structures is cumbersome and costly, typically involving heating techniques of members, such as the inner ring of a rolling bearing to be mounted, in order to provide suitable attachment and pre-stressing, while maintaining a high level of precision to ensure a correct alignment and orientation of the rolling bearing in relation to the shaft and/or support structure. As a result, the mounting process is complicated and time-consuming, and often requires auxiliary equipment for heating and alignment control measurements. Also, in the hitherto known solutions, the dismounting of the load bearing rolling bearings from the rotor shaft or from the support structures is cumbersome and time-consuming. In other words, mounting and dismounting of the rotor arrangement and the bearing typically require advanced application engineering, while posing high quality requirements on the surrounding parts of the system.
Moreover, in order to ensure that the bearing is capable of being operated under extreme conditions without extensive maintenance, relevant parts of the bearing, such as the raceways, may have to undergo a heat treatment process, such as for instance a hardening process in order to withstand high contact stresses and fatigue damages.
One example of a bearing commonly used in fluid machinery applications, such as wind turbines arrangements, is a spherical roller bearing. A spherical roller bearing is provided with a spherical geometry allowing for self-alignment of the shaft during operation (i.e. upon rotation of the shaft). By self-alignment, the angular alignment of the rotational axis of the rotating shaft may change in relation to the bearing such that an angular movement of the shaft in relation to the housing is permitted. Another example of a bearing commonly used in fluid machinery applications, such as wind turbines arrangements, is a tapered roller bearing. A tapered roller bearing (TRB) is provided with conically shaped rollers with inclined raceways. Typically, a tapered roller bearing cannot misalign. In addition, tapered roller bearings may require high preload and high accuracy on its components. Since there is a risk of generating excessive contact stresses during operation of the tapered roller bearing, there is often a prerequisite to perform advanced FEM calculations in order to provide an appropriately dimensioned bearing. One area of interest when designing tapered roller bearings is the design of the housing seats, which should be as accurate as possible to ensure that no misalignment can occur during operation of the bearing.
During operation of the rotor shaft arrangement, the axial movement of the rotating shaft must further be restricted by the roller bearing in order to provide a smooth operation and to reduce wear and damage to connected and/or surrounding equipment, such as a gear box etc. Any excessive axial play may considerably reduce the life time of the application arrangement.
Moreover, in order to provide an appropriate and a durable axial locating function of the spherical roller bearing, the size and the radial dimension of the geometry of the spherical roller bearing may be increased. By increasing the size and the radial dimension, the contact angles between the rollers and raceway in relation to the axis of the rotating shaft are increased. With respect to tapered roller bearings, the inner geometry of TRBs is designed according to radial and axial loads. The contact angles are chosen according to the load requirements. In contrast, for standard SRBs, the contact angle in ISO-series dependent is almost fixed. Further, the ISO-series dependent contact angle is selected according to the axial load requirements. This may lead to an over-dimensioning for radial loads.
Accordingly, hitherto known bearing solutions for fluid machinery applications involving an axially locating roller bearing are considered to suffer from overdesigning in relation to e.g. radial load bearing capacity. Similarly, many of those bearings are non-compact including large bearing designs in order to provide a sufficient axial load bearing capacity. In this manner, this type of bearing is considered to occupy valuable space in the fluid machinery arrangement. Furthermore, larger bearings are more expensive to produce due to high material costs, while the high bearing mass may have a negative impact on the operational efficiency by e.g. increasing the rotational inertia of the arrangement.
It therefore remains a need for a simple bearing arrangement which requires less accuracy requirements of the surrounding parts and reduced application engineering efforts, while maintaining a high capacity to withstand radial and axial loads from the rotor shaft of the fluid machinery application.